The optical field above water is not isotropic. It is important to study the directional reflectance properties of the optical field above water, which is useful for building water quality parameters retrieving models by remote sensing. The bidirectional reflectance distribution function above oceanic waters has been well studied. However, the bidirectional reflectance distribution function above inland waters is still unresolved. The in-situ measured multi-angle remote sensing reflectance above water provides valuable data for studying directional reflectance properties above water. Unfortunately, such data is almost unavailable for inland waters due to the lack of of feasible instrument. Therefore, the authors designed and manufactured a specialized device to measure in situ multi-angle remote sensing reflectance involving with a spectrometer. We carried out an experiment in Lake Taihu to measure in situ multi-angle remote sensing reflectance data with this device. Then, we analyzed the directional properties of the remote sensing reflectance above water surface of Lake Taihu, and their effects on building water quality parameters retrieving models by remote sensing. Finally, we proposed a strategy for building water quality parameters retrieving models, which could reduce the directional effects of the optical field above inland waters.